GSA Connects 2021 in Portland, Oregon

Paper No. 192-15
Presentation Time: 2:30 PM-6:30 PM


LISCOMB, J.B.1, MOJICA, G.R.1, BAILEY, C.M.1 and RICH, M.2, (1)Geology, William & Mary, Williamsburg, VA 23187, (2)Polycor Inc., Tate, GA 30177

Altered and metamorphosed ultramafic rocks, broadly known as soapstone, occur in Albemarle and Nelson counties in the eastern Blue Ridge of Virginia. Soapstone was extensively quarried near the town of Schuyler since the 1880s, but the industry declined throughout the late 20th century. In the 2010s, Polycor, a dimension stone purveyor, resumed quarrying in the Schuyler area to provide soapstone for high-end architectural uses. The origin of soapstone in the eastern Blue Ridge is enigmatic with some researchers theorizing that these are ophiolite fragments emplaced during the Taconian orogeny while other workers argue these are differentiated sills or dikes associated with Iapetan rifting during the Ediacaran. As part of a new exploration campaign, Polycor drilled ~600 meters of rock core (from 13 holes) in January 2021. Our research utilizes core logging, petrological, chemical, and structural analysis in conjunction with detailed mapping to determine the geometry and origin of the soapstone bodies in the Schuyler area.

In map view, soapstone bodies are ~1 to 8 km in length and parallel to the NNE-SSW regional trend of the eastern Blue Ridge. Soapstone bodies form tabular, sheet-like bodies up to ~100 m thick that dip 45˚ to 65˚ SE with a concordant relationship to bedding in metasedimentary rocks of the Neoproterozoic Lynchburg Group (meta-sandstone and siltstone). Soapstone consists dominantly of talc, chlorite, serpentine, carbonate minerals ± magnetite and pyrite. Texturally the rock ranges from massive to foliated. Based on handheld XRF analyses, the soapstone is composed of 40-50% SiO2, ~10% FeO, and ~30% MgO. Several zones of meta-diorite and fine-grained meta-felsite occur in some cores. These intermediate/felsic rocks form both localized layers at the top of the ultramafic bodies and thin dikes. Chlorite blackwall is common at contacts between ultramafic and intermediate/felsic rocks.

Based on the geometry and chemical trends we interpret these bodies to be differentiated sills that intruded into a thick sequence of Cryogenian to Ediacaran rift sediments formed along the highly extended Laurentian margin during Iapetan rifting. Future work will focus on the geochemistry of selected samples as well as obtaining U-Pb zircon ages of the intermediate-felsic rocks.